Experimental evidence of the Strato-rotational instability

Abstract

This experimental study is devoted to the analysis of the Strato-rotational Instability (SRI) that affects the classical cylindrical Couette flow when the fluid is stably stratified in the axial direction. In agreement with recent theoretical and numerical predictions, we describe for the first time in detail the destabilization of the stratified flow below the Rayleigh line (i.e. the stability threshold without stratification). We confirm that the unstable modes of the SRI have an helicoidal shape and that the SRI takes place as soon as the azimuthal linear velocity decreases along the radial direction as it was claimed by Shalybkov and Riidiger in 2005. A direct consequence of this departure from the Rayleigh criterion is that centrifugally stable stratified Keplerian flows, as those met in accretion disks, are unstable to the SRI.